As wireless communications standards continue to evolve to provide higher data rates, reliability, and network capacity, technologies such as carrier aggregation and multiple-input-multiple-output (MIMO) have become commonplace. Wireless communications devices utilizing carrier aggregation and/or MIMO use multiple antennas to simultaneously transmit and receive signals within different wireless operating bands. These wireless communications devices require specialized filtering circuitry to separate signals within the different wireless operating bands, which generally adds significant complexity and size to radio frequency (RF) front end circuitry within the devices.
FIG. 1 is a schematic representation of conventional RF front end circuitry 10 capable of operating in a carrier aggregation and/or MIMO configuration. The conventional RF front end circuitry 10 includes a primary antenna 12A, a secondary antenna 12B, antenna switching circuitry 14, primary transceiver circuitry 16, and secondary receiver circuitry 18. The primary transceiver circuitry 16 and the secondary receiver circuitry 18 are coupled to the primary antenna 12A and the secondary antenna 12B via the antenna switching circuitry 14. As shown in FIG. 1, the antenna switching circuitry 14 is a dual-pole, dual-throw (DPDT) switch configured to couple the primary transceiver circuitry 16 to one of the primary antenna 12A and the secondary antenna 12B, and couple the secondary receiver circuitry 18 to the antenna 12 not coupled to the primary transceiver circuitry 16. In normal operation, the primary transceiver circuitry 16 is coupled to the primary antenna 12A in order to transmit and receive primary RF transmit signals and primary RF receive signals therefrom, while the secondary receiver circuitry 18 is coupled to the secondary antenna 12B in order to receive secondary RF receive signals. However, the antenna switching circuitry 14 may swap the primary antenna 12A and the secondary antenna 12B when the performance of the secondary antenna 12B is superior to that of the primary antenna 12A. For example, the antenna switching circuitry 14 may swap the primary antenna 12A and the secondary antenna 12B when a voltage standing wave ratio (VSWR) associated with the secondary antenna 12B is smaller than a VSWR associated with the primary antenna 12A.
The secondary receiver circuitry 18 includes filtering circuitry 20, receiver switching circuitry 22, and a number of low-noise amplifiers (LNAs) 24. The filtering circuitry 20 is coupled to the antenna switching circuitry 14, while the receiver switching circuitry 22 is coupled between the filtering circuitry 20 and the LNAs 24. The filtering circuitry 20 is configured to isolate signals within a particular operating band or group of operating bands received from the antenna 12 so that they may be separately processed. The receiver switching circuitry 22 is configured to couple an output of a filter or group of filters in the filtering circuitry 20 to one of the LNAs 24, where the isolated signal is then amplified for further processing (e.g., baseband conversion). Each one of the LNAs 24 may be designed to amplify a particular operating band or group of operating bands efficiently and with low distortion.
The filtering circuitry 20 may include a number of acoustic filters 26, which may be isolated or grouped together with additional acoustic filters to form an RF multiplexer 28. In its simplest form, the filtering circuitry 20 includes an isolated acoustic filter 26 for each operating band supported by the secondary receiver circuitry 20. However, performance improvements and area reductions may be achieved by grouping the acoustic filters 26 into RF multiplexers 28. Generally, the acoustic filters are band-pass filters configured to pass one or more desired operating bands while attenuating all signals outside of the desired operating bands. The acoustic filters 26 must provide high attenuation at all frequencies outside of the desired pass-band to reduce undesirable distortion, while providing low insertion loss within the pass-band. The largest source of undesirable distortion in the conventional RF front end circuitry 10 generally comes from antenna-to-antenna coupling of primary RF transmit signals into the signal path of the secondary receiver circuitry 18. The primary RF transmit signals are high power signals compared to the secondary RF receive signals, and thus can cause many problems such as desensitization of the secondary receiver circuitry 18. Accordingly, the main purpose of each one of the acoustic filters 26 is to attenuate primary RF transmit signals in the secondary receiver signal path while passing the secondary RF receive signals with as little attenuation as possible.
As the number of operating bands supported by modern wireless communications standards continue to increase, the complexity and size of the filtering circuitry 20, the receiver switching circuitry 22, and the LNAs 24 increases in turn. Since the area of RF front end circuitry is a primary concern in portable wireless communications devices, there is a need for RF front end circuitry configured to operate in carrier aggregation and/or MIMO configurations with reduced size and complexity.